Image display monitors are being used not only in offices or households but also at sites of various kinds of professional work, such as graphic design and medical care. In particular, high-end liquid crystal monitors are being used to display a graphic design image or medical diagnostic image, since display of such images requires high-definition image quality having high reproducibility. Such a liquid crystal monitor, which is required to provide high-definition image quality having high reproducibility, attempts to enhance the reproducibility of display images by measuring an optical property of a liquid crystal screen, such as luminance, chromaticity, or the amount of light, using a physical quantity sensor such as an optical sensor, and then performing calibration on the basis of the measured data.
To enhance the reproducibility of display images, calibration must be performed every predetermined time. For this reason, a sensor unit actuating mechanism for measuring an optical property of a liquid crystal screen is integrated into a liquid crystal monitor (see Patent Document 1), or an optical measuring instrument including a sensor unit actuating mechanism for measuring an optical property of a liquid crystal screen is disposed adjacent to a bezel (frame) of a liquid crystal monitor (see Patent Document 2).
Patent Document 1 states that a movable optical measuring instrument 104 is disposed at one of the four corners of a liquid crystal display device including a rectangular liquid crystal screen 101 and a bezel 102 disposed around the liquid crystal screen 101 (FIG. 27 of the present application). Patent Document 2 shows three positions at which an optical measuring unit 108 including an optical measuring instrument 104 can be disposed on a bezel 102: at one corner of the bezel 102; at a side portion around the center of the upper-side bezel 102; and at a side portion around the center of the lateral-side bezel 102 (FIG. 28 of the present application). The optical measuring instrument 104 is a planar unit including a physical quantity sensor, such as an optical sensor, and will be referred to as a sensor unit. Both the sensor unit actuating mechanisms for screen measurement described Patent Documents 1 and 2 are mechanisms that revolve the sensor unit using an electric motor and a drive transmission mechanism, such as a gear box, in such a manner that the sensor unit draws a circle whose center is at a point around the center of one side of the bezel (frame) or on one corner of the bezel.
To meet the high-reproducibility, high-definition image quality requirement, the above-mentioned liquid crystal display devices are required to accurately measure the optical property of the display screen, such as luminance or chromaticity, without being affected by ambient external light during calibration, by placing the sensor for measuring a physical quantity, such as luminance or chromaticity, at a measurement position adjacent to the monitor screen over the monitor screen. The liquid crystal display devices are also required to have high functionality, such as the size or viewability of displayed images, and high designability, and in this regard, the thickness of the bezel is reduced to obtain a flat face. Accordingly, it is desired to prevent the sensor unit actuating mechanism from restricting the appearance and shape of the liquid crystal display device and thus impairing designability.
However, the mechanisms described in Patent Documents 1 and 2 employ a system which causes the sensor unit to leave or enter the frame or measuring instrument and revolve. Accordingly, the mechanisms use the electric motor and drive transmission mechanism so as to obtain a torque necessary to cause the arm of the sensor unit to revolve. This makes the mechanisms large-scale. In other words, there is a need to reserve space for housing the electric motor and the drive transmission mechanism, thereby forming a design limitation. Further, an increase in the size of the sensor unit actuating mechanism for screen measurement affects the designability of the liquid crystal display device.
Miniaturization or space-saving of mechanical elements has been contemplated with respect to various types of industrial products. Actuators using a shape-memory alloy wire have been commercialized as small actuators for replacing an electric motor in recent years. For example, a thinner endoscope imposes a smaller load on an object to be observed when inserted thereinto. For this reason, multiple shape-memory alloy wires having a property of contracting when heated are previously mounted on the tip of an endoscope cable; wiring is installed such that current is passed through each of these shape-memory alloy wires; and a predetermined one of these shape-memory alloy wires generates Joule heat when energized and thus contracts; and consequently the tip of the endoscope cable is bent in a predetermined direction. Such an electric actuator enables traditional small machines incapable of incorporating an electric motor to have a motion function. Accordingly, various efforts to utilize such an electric actuator have been made, and related patent applications have been filed (Patent Documents 3, 4).
Patent Document 3 discloses an actuator which actuates a crank mechanism by combining two shape-memory alloy wires, the crank mechanism, and an extension spring attached to an actuator member of the crank mechanism and then energizing one of the shape-memory alloy wires to contract it and thus moves the actuator member to a predetermined stable position using the tensile force of the extension spring; and actuates the crank mechanism toward the opposite side by energizing the other shape-memory alloy wire to contract it and thus moves the actuator member to a predetermined opposite stable position using the tensile force of the extension spring. Patent Document 4 discloses an actuator which actuates an actuator member of a crank mechanism by combining two shape-memory alloy wires, the crank mechanism, and a pressing spring and then energizing one of the shape-memory alloy wires to contract it and thus moves the actuator member to a predetermined stable position using the pressing force of the pressing spring attached to the outside of the crank mechanism; and actuates the actuator member toward the opposite side by energizing the other shape-memory alloy wire to contract it and thus moves the actuator member to a predetermined opposite stable position using the pressing force of the extension spring. The electric actuators described in Patent Documents 3 and 4 have a configuration in which the actuator member of the crank mechanism revolves in a manner to draw an arc and performs a switching operation. However, these Patent Documents do not disclose any specific applications or the like except for such a configuration.